Fail-safe dry friction clutch for a coolant pump

ABSTRACT

A fail-safe friction clutch assembly for a vehicle accessory, particularly to drive a vehicle cooling pump, and more particularly as part of a dual mode drive for a cooling pump, together with an electric motor. The friction clutch assembly includes a friction plate member connected to a central rotatable shaft member used for operating the vehicle accessory. A pair of friction lining members are positioned on opposite sides of the friction plate member. An armature member is spring biased to axially force the friction plate member and friction lining member against a housing or cover which is rotating at input speed. A solenoid assembly is used to overcome the spring bias and pull the armature and friction plate member away from the housing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser. No. 14/135,280 filed on Dec. 19, 2013, which is a non-provisional of U.S. Provisional Application Ser. No. 61/745,647 filed on Dec. 24, 2012. This application is also related to U.S. Patent Application Ser. No. 61/474,862 and U.S. Patent Application Ser. No. 61/474,928, both filed on Apr. 13, 2011.

TECHNICAL FIELD

Friction clutch assemblies, particularly for hybrid coolant pumps, are disclosed.

BACKGROUND

Water pumps are used in water cooled engines, primarily for operation of vehicles such as automobiles and trucks with internal combustion engines. The water pumps are typically driven by a belt attached to the crankshaft of the engine and thus operate at some percentage of engine speed. The pumps have an impeller that is used to circulate the engine coolant from the engine to the radiator and back in order to keep the coolant within acceptable temperature limits.

Efforts are being made today to reduce the power consumption of engine accessories, such as water pumps, in order to improve fuel economy and reduce emissions. It would thus be preferable if such accessories, including water pumps, could be made to operate at variable speeds or with less power in order to reduce the load on the engine and, in turn, improve fuel economy and reduce undesirable emissions from the engine.

SUMMARY OF THE INVENTION

A vehicle water pump assembly having an improved dry friction clutch mechanism is disclosed. The water pump preferably has two modes of operation, a first mode mechanical driven by an engine belt, and a second mode operated by an electric motor, such as a brushless DC (BLDC) motor. The components for the two modes of operation are included as part of a multi-component assembly that includes a pulley member. The pulley is turned at input speed by an engine belt positioned on the pulley member. A shaft connected to the impeller of the water pump is positioned in the assembly and is controlled by either the mechanical or electrical operation, or both, depending on certain factors.

The friction clutch assembly is positioned inside the multi-component assembly to selectively allow operation of the water pump mechanically by the pulley member. The dry friction clutch assembly is activated by turning on/off a solenoid. When the solenoid is off for any reason, the clutch will be engaged, and thus the clutch is fail-safe. When the solenoid is off, a number of coil springs push an armature plate which clamps a friction plate between the armature plate and a cover member. Torque is transferred through both sides of the friction plate. The clutch is disengaged by turning on the solenoid.

When the solenoid is on, the solenoid force overcomes the force of the coil springs and pulls the armature plate back against the pulley, and a return spring pushes the friction plate away from the cover and holds it against a stop, creating air gaps on both sides of the friction plate. When the clutch is disengaged, the input (pulley) and output (shaft) are disconnected, eliminating interaction (e.g. bearing drag) between the input and output.

The water pump is normally driven by the electric motor throughout most of its range of operation. Where peak cooling requirements are needed, the mechanical mode of operation takes over and the water pump can be driven directly by the pulley member. In some circumstances, both the mechanical and electrical operations can be performed at the same time.

Further objects, features and benefits of the invention are set forth below in the following description of the invention when viewed in combination with the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vehicle water pump assembly which can incorporate the present invention.

FIG. 2 is a cross-sectional view of the assembly shown in FIG. 1 and featuring an embodiment of the present invention.

FIG. 3A and 3B are exploded views of the components of the assembly as shown in FIG. 2.

FIG. 4 is an enlarged cross-sectional view of the assembly shown in FIGS. 2-3 with the components shown in the solenoid disengaged position.

FIG. 5 is an enlarged cross-sectional view of the assembly shown in FIGS. 2-3 with the components shown in the solenoid engaged position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purpose of promoting and understanding the principles of the present invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe them. It will nevertheless be understood that no limitation as to the scope of the invention is hereby intended. The invention includes any alternatives and other modifications in the illustrated devices and described methods and further applications of the principles of the invention which would normally occur to persons or ordinary skill in the art to which the invention relates.

The present inventions described herein relate to friction clutch assemblies particularly used for coolant pumps which circulate the coolant in an engine, such as an automobile internal combustion engine. (The terms “water pump” and “coolant pump” are used interchangeably herein.) The present invention, however, can also be used for other engine accessory devices.

The preferred embodiment of the present invention as described herein is particularly adapted for use with trucks, passenger cars and off-highway vehicles, and will be described with respect to its use in a dual mode coolant pump. In accordance with a preferred embodiment, the electric motor is a brushless DC (BLDC) motor. For the mechanical mode of operation, the water pump is driven by an engine belt, such as a serpentine accessory belt, attached to the crankshaft of the engine.

As a dual mode coolant pump, the pump is electrically driven under most conditions. However, it also can be mechanically engaged where more cooling is required. Thus, when the vehicle is being driven under most normal conditions, the water pump is being driven and operated by the electric motor.

During “worst case” cooling conditions, such as when the vehicle is heavily loaded, when it is pulling a trailer, or when it is going up hill in the summertime, etc., the water pump is adapted to be mechanically driven by the belt directly from the engine. This provides the necessary cooling under such circumstances. In some circumstances, it may be necessary or possible to perform both modes of operation.

A hybrid (dual mode) water pump embodiment with a friction clutch assembly in accordance with the present invention is shown in FIGS. 1-5 and referred to generally by the reference numeral 20. The hybrid water pump includes a motor housing 22, a solenoid housing 24, a pulley member 26 and a cover member 28. A central shaft member 30 is rotated by the pump 20 which operates the water pump impeller 32. As shown, the pulley member has a smooth outer surface 27 on which an engine belt (not shown) is positioned. The outer surface of the pulley member could also comprise circumferential grooves for mating with an engine belt with corresponding grooves.

A cross-sectional view of the water pump assembly 20 is shown in FIG. 2 and an exploded view of the components of the water pump assembly 20 is shown in FIG. 3. Enlarged views showing the friction clutch mechanism in the deactivated and activated modes of operation are shown in FIGS. 4 and 5.

The water pump assembly has an impeller shaft 30 which is positioned within the assembly and is attached to a water pump impeller 32. The impeller shaft 30 is held in place in the multi-component assembly by bearings 34 and 36. A coolant seal 38 is used to prevent coolant in the pump from leaking into the motor housing.

A motor 50 is positioned inside the motor housing 22. The motor 50 includes a rotor carrier 52, magnets 53, and a stator 54. Magnets 53 are bonded to the rotor carrier 52 and together form the rotor of the motor. The motor 50 is preferably a brushless DC (BLDC) electric motor. The rotor 52 is securely attached, e. g. press fitted, to the shaft 30, which causes the shaft, and thus the impeller 32, to rotate when the motor 50 is operated. Electricity to the motor 50 is supplied by an electrical source (not shown).

The motor housing 22 has a plurality of mounts, only two of which 23, 25, are shown in the drawings. The mounts have openings for attachment of the water pump assembly 20 inside the engine compartment of a vehicle.

The friction clutch assembly is designated generally by the reference numeral 60. The friction clutch assembly generally comprises an armature plate 62, a friction plate 64, and two annular rings of friction material 66 and 68. The armature plate 62 is preferably made of a magnetic metal material, such as low carbon steel. The friction plate 64 is preferably made of a non-magnetic material, such as stainless steel. The friction material 66 and 68 can be any conventional friction materials used in friction clutches today, and can be complete rings, segments of rings, or simply pieces of friction material positioned generally where rings 66 and 68 are positioned in the drawings. Preferably, the friction materials 66, 68 are bonded to the friction plate 64 using a bonding agent.

The cover member 28 which preferably is made of a non-magnetic material, such as stainless steel, is connected directly to the pulley member 26 by a plurality of connecting pin members, such as fasteners or bolts 72. The ends of the fasteners can be threaded (as shown particularly in FIG. 2) for mating with corresponding mating threads in openings 74 in the pulley member 26. Thus, when the pulley is rotated by an engine belt (not shown); the cover member 28 rotates at the same input speed.

The pulley member 26 is preferably made of a magnetic metal material, such as low carbon steel. The pulley member rotates freely around bearings 80. Although the bearings can be of any type that will have sufficient durability and performance, a pair of stacked bearings can be utilized, as shown in the drawings.

The operation of the friction clutch assembly is performed by a solenoid assembly 90. The solenoid assembly includes a solenoid coil 92 which is positioned in the solenoid housing 24. The solenoid coil member comprises a donut-shaped coil of copper wires, while the solenoid housing is preferably made of a magnetic material, such as low carbon steel. The solenoid coil member 92 is potted in the solenoid housing 24.

The solenoid housing 24 is independently positioned in the water pump assembly by use of bearing 36. The bearing 36 allows the shaft member 30 to rotate freely relative to the solenoid housing 24.

The solenoid housing 24 is connected directly to the motor housing 22 by, for example, a press fit and/or a series of fastener members 29. In production, several different ways can be used to anchor or fix the solenoid housing 24 to the motor housing 22.

The nut member 102 is threaded, or otherwise firmly fixed, on the end of the shaft member 30. The friction plate member 64 is connected, such as being keyed, to the nut member 102. As shown in FIG. 3A, the nut member has a plurality of spline members 103 which fit within corresponding notches 65 in the center of the friction plate member 64. In this manner, the nut and friction plate members rotate with the shaft member 30. The nut member 102 and the shaft member 30 firmly clamp the stop member 100 and the bearing member 36 together. The shaft member 30 and all components fixed on it are positioned axially by the bearing member 36. The stop member 100 is preferably made of a non-magnetic material, such as stainless steel.

To fix the bearing member 36 in an axial position inside the solenoid housing 24, a wave spring member 104 and bearing retainer member 106 are utilized. The bearing retainer member 106 is threadedly affixed to the solenoid housing as shown by reference number 101 (see FIG. 4).

The stop member 100 is utilized to stop the axial movement of the friction plate member 64 when the solenoid assembly 90 is energized, as explained below. A return spring 110 is positioned between the nut member 102 and the friction plate member 64 and acts to return the friction plate member 64 to its mechanical disengaged position when the solenoid assembly 90 is actuated.

As indicated, the water pump impeller 32 is normally driven by the electric motor 50. The electric motor and the solenoid coil are electrically powered through a circuit board (not shown). Electrical leads and wires can be insert molded in the motor housing 22 in order to carry the electrical signals to the electric motor 50 and solenoid coil member 92. The circuit board further communicates with the electronic control unit (ECU) of the vehicle through the vehicle communication network such as a CAN network. The water pump assembly controller circuit board could also be positioned inside the motor housing 22 possibly having a donut shape.

The speed of the motor and thus the water pump is selected according to the cooling required for the engine. Sensors feed relevant data to the ECU which then sends a signal to the pump controller requesting the desired speed. The pump controller then determines whether the desired speed is best achieved using the electric motor or by engaging the friction clutch and driving the impeller directly from the pulley.

When the water pump is being driven solely by the electric motor 50, the friction clutch assembly is held in a disengaged position by the solenoid assembly 90. This is shown in FIG. 5. When the solenoid coil member 92 is electrically activated, a flux circuit 120 is created which acts to pull the armature plate 62 toward the solenoid coil member overcoming the force of the coil spring members 108. With the armature plate 62 pulled toward the solenoid, the return spring 110 holds the friction plate 64 against the stop member 100. In this condition, the friction materials on the friction plate 64 are not in contact with either the cover member 28 or the armature plate 62.

The number of coil springs 108 and their biasing force is determined according to the force needed in the assembly. Six coil springs 108 are shown in the drawings, but there can be more or less than this amount depending on the force needed.

In this electrical mode of operation, there are air gaps on both sides of the friction materials on the friction plate, and the input (pulley member) and output (shaft member) are completely disconnected. This eliminates any interaction, such as bearing drag between the input and output.

In order to create an appropriate flux circuit 120, the pulley member 26 has a plurality of openings 115 which create air gaps. The openings 115 essentially form an annular open ring. With the air gaps, the pulley member is for electromagnetic purposes, essentially an outer annular ring 116 and a separated annular inner ring 118. (This is best shown in FIG. 3B.)

The flux circuit 120 is shown in FIG. 5. It runs through the solenoid housing 24, the belt engaging portion of the pulley member 26, outer annular ring portion of the pulley member 26, and then jumps to the armature plate member 62 and then back to the inner annular ring portion of the pulley member 26 where it returns to the solenoid housing. This circuit pulls the armature member tightly to the pulley member such that the armature member rotates with the pulley member and at the same speed.

FIG. 4 depicts the situation where the solenoid assembly 90 is not activated. This causes the water pump to be driven mechanically by an engine belt and the electric motor 50 can be turned off. In this situation, coil springs 108 force the armature member 62 in a direction away from the pulley member and away from the solenoid assembly. This causes the armature member 62 to contact the friction member 68 which in turn forces the friction member 66 to contact the inner surface 28A of the cover member 28. Since the armature member, pulley member and cover member are all fixed together, this causes the shaft member 30 to rotate at the same speed.

A path of torque transfer which mechanically rotates the shaft member is shown by arrows 130 in FIG. 4. In the engaged clutch, the friction plate member is clamped between the cover member and armature member and torque is transferred through both sides of the friction plate. There also is a torque transfer path from the pulley member 26, through the fastener 72, the armature plate member 62, the friction plate member 64, the nut member 100 and to the shaft 30.

It is common in automotive accessories such as air conditioning compressors, pumps, etc. to use spring engaged, electromagnetically disengaged clutches to selectively turn on and off the drive to the accessory component. This is typically done to conserve energy when the device is not needed. These devices are typically designed to be spring engaged so the accessory device is powered in the event of a control failure such as a loss of electrical power. This is done to provide “Fail-Safe” functionality meaning that the device defaults to its “on” state when it is unpowered.

As indicated above, the present invention provides a “fail-safe” friction clutch design. If the electrical system of the coolant pump were to fail, the solenoid would be de-energized allowing the coil springs to force the friction clutch assembly to become engaged. Therefore the pump would operate in mechanical mode with the impeller driven by the pulley member through the clutch assembly, thus preventing overheating.

Although the invention has been described with respect to preferred embodiments, it is to be also understood that it is not to be so limited since changes and modifications can be made therein which are within the full scope of this invention as detailed by the following claims. 

What is claimed is:
 1. A dual mode drive device for a vehicle accessory comprising: (a) a housing member; (b) rotatable shaft member in said housing for selectively operating said vehicle accessory; (c) an electric motor in said housing member for selectively rotating said shaft member and operating said vehicle accessory; and (d) a friction clutch assembly in said housing member for assisting in selectively operating said vehicle accessory, said friction clutch assembly comprising: a solenoid assembly with a solenoid coil member; a pulley member rotatable at input speed; a housing cover member attached to said pulley member and rotatable therewith; an axially movable magnetic armature member; spring members for biasing said armature member axially away from said solenoid assembly; friction plate member connected to said central shaft member and rotatable therewith; a first friction lining member positioned on a first surface of said friction plate member and adjacent said armature member; and a second friction lining member positioned on a second and opposite surface of said friction plate member and adjacent said housing cover member; wherein when said solenoid assembly is not electrically actuated, said spring members force said armature member and said friction plate member axially in a direction toward said housing cover member wherein said second friction lining member contacts said housing cover member causing said friction plate member and said central shaft member to rotate at input speed.
 2. The friction clutch assembly as set forth in claim 1 wherein said solenoid assembly is not electrically actuated, said armature member is forced against said first friction lining member, causing said armature member to rotate at input speed.
 3. The friction clutch assembly as set forth in claim 1 wherein said housing member comprises a cover member.
 4. The friction clutch assembly as set forth in claim 1 wherein said electric motor is a brushless DC motor.
 5. The friction clutch assembly as set forth in claim 1 wherein said vehicle accessory is a water pump.
 6. The friction clutch assembly as set forth in claim 1 wherein said rotatable shaft member is attached to a water pump impeller member and said vehicle accessory is a water pump.
 7. The friction clutch assembly as set forth in claim 1 wherein said spring members comprise a plurality of coil spring members.
 8. The friction clutch assembly as set forth in claim 1 wherein said first and second friction lining members each comprise annular rings of friction lining material.
 9. The friction clutch assembly as set forth in claim 1 further comprising a return spring member for biasing said friction plate member axially away from said housing cover member.
 10. The friction clutch assembly as set forth in claim 1 wherein said pulley member comprises a plurality of openings forming an insulating air gap between an inner ring portion and an outer ring portion.
 11. The friction clutch assembly as set forth in claim 1 wherein the flux path for axially moving said armature member when the solenoid assembly is activated comprises a path through said solenoid assembly, said pulley member, said armature member, back to said pulley member and then back to said solenoid assembly.
 12. The friction clutch assembly as set forth in claim 1 wherein said pulley member and said housing cover member are attached together by a plurality of fastener members.
 13. The friction clutch assembly as set forth in claim 12 wherein said fastener members are bolts.
 14. The friction clutch assembly as set forth in claim 1 wherein the connection between said friction plate member and said central shaft member comprises a nut member. 